Method and system for incrementally moving teeth

ABSTRACT

A system for repositioning teeth comprises a plurality of individual appliances. The appliances are configured to be placed successively on the patient&#39;s teeth and to incrementally reposition the teeth from an initial tooth arrangement, through a plurality of intermediate tooth arrangements, and to a final tooth arrangement. The system of appliances is usually configured at the outset of treatment so that the patient may progress through treatment without the need to have the treating professional perform each successive step in the procedure.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is a continuation of application Ser. No.09/298,268, filed Apr. 23, 1999, which was a division of applicationSer. No. 08/947,080, filed Oct. 8, 1997, which was claims benefit ofprovisional application Ser. No. 60/050,342, filed on Jun. 20, 1997, thefull disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is related generally to the field oforthodontics. More particularly, the present invention is related to amethod and system for incrementally moving teeth from an initial tootharrangement to a final tooth arrangement.

[0004] Repositioning teeth for aesthetic or other reasons isaccomplished conventionally by wearing what are commonly referred to as“braces.” Braces comprise a variety of appliances such as brackets,archwires, ligatures, and O-rings. Attaching the appliances to apatient's teeth is a tedious and time consuming enterprise requiringmany meetings with the treating orthodontist. Consequently, conventionalorthodontic treatment limits an orthodontist's patient capacity andmakes orthodontic treatment quite expensive.

[0005] Before fastening braces to a patient's teeth, at least oneappointment is typically scheduled with the orthodontist, dentist,and/or X-ray laboratory so that X-rays and photographs of the patient'steeth and jaw structure can be taken. Also during this preliminarymeeting, or possibly at a later meeting, an alginate mold of thepatient's teeth is typically made. This mold provides a model of thepatient's teeth that the orthodontist uses in conjunction with theX-rays and photographs to formulate a treatment strategy. Theorthodontist then typically schedules one or more appointments duringwhich braces will be attached to the patient's teeth.

[0006] At the meeting during which braces are first attached, the teethsurfaces are initially treated with a weak acid. The acid optimizes theadhesion properties of the teeth surfaces for brackets and bands thatare to be bonded to them. The brackets and bands serve as anchors forother appliances to be added later. After the acid step, the bracketsand bands are cemented to the patient's teeth using a suitable bondingmaterial. No force-inducing appliances are added until the cement isset. For this reason, it is common for the orthodontist to schedule alater appointment to ensure that the brackets and bands are well bondedto the teeth.

[0007] The primary force-inducing appliance in a conventional set ofbraces is the archwire. The archwire is resilient and is attached to thebrackets by way of slots in the brackets. The archwire links thebrackets together and exerts forces on them to move the teeth over time.Twisted wires or elastomeric O-rings are commonly used to reinforceattachment of the archwire to the brackets. Attachment of the archwireto the brackets is known in the art of orthodontia as “ligation” andwires used in this procedure are called “ligatures.” The elastomericO-rings are called “plastics.”

[0008] After the archwire is in place, periodic meetings with theorthodontist are required, during which the patient's braces will beadjusted by installing a different archwire having differentforce-inducing properties or by replacing or tightening existingligatures. Typically, these meetings are scheduled every three to sixweeks.

[0009] As the above illustrates, the use of conventional braces is atedious and time consuming process and requires many visits to theorthodontist's office. Moreover, from the patient's perspective, the useof braces is unsightly, uncomfortable, presents a risk of infection, andmakes brushing, flossing, and other dental hygiene procedures difficult.

[0010] For these reasons, it would be desirable to provide alternativemethods and systems for repositioning teeth. Such methods and systemsshould be economical, and in particular should reduce the amount of timerequired by the orthodontist in planning and overseeing each individualpatient. The methods and systems should also be more acceptable to thepatient, in particular being less visible, less uncomfortable, lessprone to infection, and more compatible with daily dental hygiene. Atleast some of these objectives will be met by the methods and systems ofthe present invention described hereinafter.

[0011] 2. Description of the Background Art

[0012] Tooth positioners for finishing orthodontic treatment aredescribed by Kesling in the Am. J Orthod. Oral. Surg. 31:297-304(1945)and 32:285-293 (1946). The use of silicone positioners for thecomprehensive orthodontic realignment of a patient's teeth is describedin Warunek et al. (1989) J. Clin. Orthod. 23:694-700. Clear plasticretainers for finishing and maintaining tooth positions are commerciallyavailable from Raintree Essix, Inc., New Orleans, La. 70125, andTru-Tain Plastics, Rochester, Minn. 55902. The manufacture oforthodontic positioners is described in U.S. Pat. Nos. 5,186,623;5,059,118; 5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.

[0013] Other publications describing the fabrication and use of dentalpositioners include Kleemann and Janssen (1996) J. Clin. Orthodon.30:673-680; Cureton (1996) J. Clin. Orthodon. 30:390-395; Chiappone(1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971) Am. J.Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics 58:351-366;and Cottingham (1969) Am. J. Orthodontics 55:23-31.

[0014] Kuroda et al. (1996) Am. J. Orthodontics 110:365-369 describes amethod for laser scanning a plaster dental cast to produce a digitalimage of the cast. See also U.S. Pat. No. 5,605,459.

[0015] U.S. Pat. Nos. 5,533,895; 5,474,448; 5,454,717; 5,447,432;5,431,562; 5,395,238; 5,368,478; and 5,139,419, assigned to OrmcoCorporation, describe methods for manipulating digital images of teethfor designing orthodontic appliances.

[0016] U.S. Pat. No. 5,011,405 describes a method for digitally imaginga tooth and determining optimum bracket positioning for orthodontictreatment. Laser scanning of a molded tooth to produce athree-dimensional model is described in U.S. Pat. No. 5,338,198. U.S.Pat. No. 5,452,219 describes a method for laser scanning a tooth modeland milling a tooth mold. Digital computer manipulation of toothcontours is described in U.S. Pat. Nos. 5,607,305 and 5,587,912.Computerized digital imaging of the jaw is described in U.S. Pat. Nos.5,342,202 and 5,340,309. Other patents of interest include U.S. Pat.Nos. 5,549,476; 5,382,164; 5,273,429; 4,936,862; 3,860,803; 3,660,900;5,645,421; 5,055,039; 4,798,534; 4,856,991; 5,035,613; 5,059,118;5,186,623; and 4,755,139.

SUMMARY OF THE INVENTION

[0017] The present invention provides improved methods and systems forrepositioning teeth from an initial tooth arrangement to a final tootharrangement. Repositioning is accomplished with a system comprising aseries of appliances configured to receive the teeth in a cavity andincrementally reposition individual teeth in a series of at least threesuccessive steps, usually including at least four successive steps,often including at least ten steps, sometimes including at leasttwenty-five steps, and occasionally including forty or more steps. Mostoften, the methods and systems will reposition teeth in from ten totwenty-five successive steps, although complex cases involving many ofthe patient's teeth may take forty or more steps. The successive use ofa number of such appliances permits each appliance to be configured tomove individual teeth in small increments, typically less than 2 mm,preferably less than 1 mm, and more preferably less than 0.5 mm. Theselimits refer to the maximum linear translation of any point on a toothas a result of using a single appliance. The movements provided bysuccessive appliances, of course, will usually not be the same for anyparticular tooth. Thus, one point on a tooth may be moved by aparticular distance as a result of the use of one appliance andthereafter moved by a different distance and/or in a different directionby a later appliance.

[0018] The individual appliances will preferably comprise a polymericshell having the teeth-receiving cavity formed therein, typically bymolding as described below. Each individual appliance will be configuredso that its tooth-receiving cavity has a geometry corresponding to anintermediate or end tooth arrangement intended for that appliance. Thatis, when an appliance is first worn by the patient, certain of the teethwill be misaligned relative to an undeformed geometry of the appliancecavity. The appliance, however, is sufficiently resilient to accommodateor conform to the misaligned teeth, and will apply sufficient resilientforce against such misaligned teeth in order to reposition the teeth tothe intermediate or end arrangement desired for that treatment step.

[0019] Systems according to the present invention will include at leasta first appliance having a geometry selected to reposition a patient'steeth from the initial tooth arrangement to a first intermediatearrangement where individual teeth will be incrementally repositioned.The system will further comprise at least one intermediate appliancehaving a geometry selective to progressively reposition teeth from thefirst intermediate arrangement to one or more successive intermediatearrangements. The system will still further comprise a final appliancehaving a geometry selected to progressively reposition teeth from thelast intermediate arrangement to the desired final tooth arrangement. Insome cases, it will be desirable to form the final appliance or severalappliances to “over correct” the final tooth position, as discussed inmore detail below.

[0020] As will be described in more detail below in connection with themethods of the present invention, the systems may be planned and allindividual appliances fabricated at the outset of treatment, and theappliances may thus be provided to the patient as a single package orsystem. The order in which the appliances are to be used will be clearlymarked, (e.g. by sequential numbering) so that the patient can place theappliances over his or her teeth at a frequency prescribed by theorthodontist or other treating professional. Unlike braces, the patientneed not visit the treating professional every time an adjustment in thetreatment is made. While the patients will usually want to visit theirtreating professionals periodically to assure that treatment is goingaccording to the original plan, eliminating the need to visit thetreating professional each time an adjustment is to be made allows thetreatment to be carried out in many more, but smaller, successive stepswhile still reducing the time spent by the treating professional withthe individual patient. Moreover, the ability to use polymeric shellappliances which are more comfortable, less visible, and removable bythe patient, greatly improves patient compliance, comfort, andsatisfaction.

[0021] According to a method of the present invention, a patient's teethare repositioned from an initial tooth arrangement to a final tootharrangement by placing a series of incremental position adjustmentappliances in the patient's mouth. Conveniently, the appliances are notaffixed and the patient may place and replace the appliances at any timeduring the procedure. The first appliance of the series will have ageometry selected to reposition the teeth from the initial tootharrangement to a first intermediate arrangement. After the firstintermediate arrangement is approached or achieved, one or moreadditional (intermediate) appliances will be successively placed on theteeth, where such additional appliances have geometries selected toprogressively reposition teeth from the first intermediate arrangementthrough successive intermediate arrangement(s). The treatment will befinished by placing a final appliance in the patient's mouth, where thefinal appliance has a geometry selected to progressively repositionteeth from the last intermediate arrangement to the final tootharrangement. The final appliance or several appliances in the series mayhave a geometry or geometries selected to over correct the tootharrangement, i.e. have a geometry which would (if fully achieved) moveindividual teeth beyond the tooth arrangement which has been selected asthe “final.” Such over correction may be desirable in order to offsetpotential relapse after the repositioning method has been terminated,i.e. to permit some movement of individual teeth back toward theirpre-corrected positions. Over correction may also be beneficial to speedthe rate of correction, i.e. by having an appliance with a geometry thatis positioned beyond a desired intermediate or final position, theindividual teeth will be shifted toward the position at a greater rate.In such cases, treatment can be terminated before the teeth reach thepositions defined by the final appliance or appliances. The method willusually comprise placing at least two additional appliances, oftencomprising placing at least ten additional appliances, sometimes placingat least twenty-five additional appliances, and occasionally placing atleast forty or more additional appliances. Successive appliances will bereplaced when the teeth either approach (within a preselected tolerance)or have reached the target end arrangement for that stage of treatment,typically being replaced at an interval in the range from 2 days to 20days, usually at an interval in the range from 5 days to 10 days.

[0022] Often, it may be desirable to replace the appliances at a timebefore the “end” tooth arrangement of that treatment stage is actuallyachieved. It will be appreciated that as the teeth are graduallyrepositioned and approach the geometry defined by a particularappliance, the repositioning force on the individual teeth will diminishgreatly. Thus, it may be possible to reduce the overall treatment timeby replacing an earlier appliance with the successive appliance at atime when the teeth have been only partially repositioned by the earlierappliance. Thus, the FDDS can actually represent an over correction ofthe final tooth position. This both speeds the treatment and can offsetpatient relapse.

[0023] In general, the transition to the next appliance can be based ona number of factors. Most simply, the appliances can be replaced on apredetermined schedule or at a fixed time interval (i.e. number of daysfor each appliance) determined at the outset based on an expected ortypical patient response. Alternatively, actual patient response can betaken into account, e.g. a patient can advance to the next appliancewhen that patient no longer perceives pressure on their teeth from acurrent appliance, i.e. the appliance they have been wearing fits easilyover the patient's teeth and the patient experiences little or nopressure or discomfort on his or her teeth. In some cases, for patientswhose teeth are responding very quickly, it may be possible for atreating professional to decide to skip one or more intermediateappliances, i.e. reduce the total number of appliances being used belowthe number determined at the outset. In this way, the overall treatmenttime for a particular patient can be reduced.

[0024] In another aspect, methods of the present invention compriserepositioning teeth using appliances comprising polymeric shells havingcavities shaped to receive and resiliently reposition teeth to produce afinal tooth arrangement. The present invention provides improvements tosuch methods which comprise determining at the outset of treatmentgeometries for at least three of the appliances which are to be wornsuccessively by a patient to reposition teeth from an initial tootharrangement to the final tooth arrangement. Preferably, at least fourgeometries will be determined in the outset, often at least tengeometries, frequently at least twenty-five geometries, and sometimesforty or more geometries. Usually, the tooth positions defined by thecavities in each successive geometry differ from those defined by theprior geometry by no more than 2 mm, preferably no more than 1 mm, andoften no more than 0.5 mm, as defined above.

[0025] In yet another aspect, methods are provided for producing adigital data set representing a final tooth arrangement. The methodscomprise providing an initial data set representing an initial tootharrangement, and presenting a visual image based on the initial dataset. The visual image is then manipulated to reposition individual teethin the visual image. A final digital data set is then produced whichrepresents the final tooth arrangement with repositioned teeth asobserved in the visual image. Conveniently, the initial digital data setmay be provided by conventional techniques, including digitizing X-rayimages, images produced by computer-aided tomography (CAT scans), imagesproduced by magnetic resonance imaging (MRI), and the like. Preferably,the images will be three-dimensional images and digitization may beaccomplished using conventional technology. Usually, the initial digitaldata set is provided by producing a plaster cast of the patient's teeth(prior to treatment) by conventional techniques. The plaster cast soproduced may then be scanned using laser or other scanning equipment toproduce a high resolution digital representation of the plaster cast ofthe patient's teeth. Use of the plaster cast is preferred since it doesnot expose the patient to X-rays or subject the patient to theinconvenience of an MRI scan.

[0026] Once the digital data set is acquired, an image can be presentedand manipulated on a suitable computer system equipped withcomputer-aided design software, as described in greater detail below.The image manipulation will usually comprise defining boundaries aboutat least some of the individual teeth, and causing the images of theteeth to be moved relative to the jaw and other teeth by manipulation ofthe image via the computer. The image manipulation can be done entirelysubjectively, i.e. the user may simply reposition teeth in anaesthetically and/or therapeutically desired manner based on observationof the image alone. Alternatively, the computer system could be providedwith rules and algorithms which assist the user in repositioning theteeth. In some instances, it will be possible to provide rules andalgorithms which reposition the teeth in a fully automatic manner, i.e.without user intervention. Once the individual teeth have beenrepositioned, a final digital data set representing the desired finaltooth arrangement will be generated and stored.

[0027] A preferred method for determining the final tooth arrangement isfor the treating professional to define the final tooth positions, e.g.by writing a prescription. The use of prescriptions for defining thedesired outcomes of orthodontic procedures is well known in the art.When a prescription or other final designation is provided, the imagecan then be manipulated to match the prescription. In some cases, itwould be possible to provide software which could interpret theprescription in order to generate the final image and thus the digitaldata set representing the final tooth arrangement.

[0028] In yet another aspect, methods according to the present inventionare provided for producing a plurality of digital data sets representinga series of discrete tooth arrangements progressing from an initialtooth arrangement to a final tooth arrangement. Such methods compriseproviding a digital data set representing an initial tooth arrangement(which may be accomplished according to any of the techniques set forthabove). A digital data set representing a final tooth arrangement isalso provided. Such final digital data set may be determined by themethods described previously. The plurality of successive digital datasets are then produced based on the initial digital data set and thefinal digital data set. Usually, the successive digital data sets areproduced by determining positional differences between selectedindividual teeth in the initial data set and in the final data set andinterpolating said differences. Such interpolation may be performed overas many discrete stages as may be desired, usually at least three, oftenat least four, more often at least ten, sometimes at least twenty-five,and occasionally forty or more. Many times, the interpolation will belinear interpolation for some or all of the positional differences.Alternatively, the interpolation may be non-linear. The positionaldifferences will correspond to tooth movements where the maximum linearmovement of any point on a tooth is 2 mm or less, usually being 1 mm orless, and often being 0.5 mm or less.

[0029] Often, the user will specify certain target intermediate tootharrangements, referred to as “key frames,” which are incorporateddirectly into the intermediate digital data sets. The methods of thepresent invention then determine successive digital data sets betweenthe key frames in the manner described above, e.g. by linear ornon-linear interpolation between the key frames. The key frames may bedetermined by a user, e.g. the individual manipulating a visual image atthe computer used for generating the digital data sets, or alternativelymay be provided by the treating professional as a prescription in thesame manner as the prescription for the final tooth arrangement.

[0030] In still another aspect, methods according to the presentinvention provide for fabricating a plurality of dental incrementalposition adjustment appliances. Said methods comprise providing aninitial digital data set, a final digital data set, and producing aplurality of successive digital data sets representing the targetsuccessive tooth arrangements, generally as just described. The dentalappliances are then fabricated based on at least some of the digitaldata sets representing the successive tooth arrangements. Preferably,the fabricating step comprises controlling a fabrication machine basedon the successive digital data sets to produce successive positivemodels of the desired tooth arrangements. The dental appliances are thenproduced as negatives of the positive models using conventional positivepressure or vacuum fabrication techniques. The fabrication machine maycomprise a stereolithography or other similar machine which relies onselectively hardening a volume of non-hardened polymeric resin byscanning a laser to selectively harden the resin in a shape based on thedigital data set. Other fabrication machines which could be utilized inthe methods of the present invention include tooling machines and waxdeposition machines.

[0031] In still another aspect, methods of the present invention forfabricating a dental appliance comprise providing a digital data setrepresenting a modified tooth arrangement for a patient. A fabricationmachine is then used to produce a positive model of the modified tootharrangement based on the digital data set. The dental appliance is thenproduced as a negative of the positive model. The fabrication machinemay be a stereolithography or other machine as described above, and thepositive model is produced by conventional pressure or vacuum moldingtechniques.

[0032] In a still further aspect, methods for fabricating a dentalappliance according to the present invention comprise providing a firstdigital data set representing a modified tooth arrangement for apatient. A second digital data set is then produced from the firstdigital data set, where the second data set represents a negative modelof the modified tooth arrangement. The fabrication machine is thencontrolled based on the second digital data set to produce the dentalappliance. The fabrication machine will usually rely on selectivelyhardening a non-hardened resin to produce the appliance. The appliancetypically comprises a polymeric shell having a cavity shape to receiveand resiliently reposition teeth from an initial tooth arrangement tothe modified tooth arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1A illustrates a patient's jaw and provides a generalindication of how teeth may be moved by the methods and apparatus of thepresent invention.

[0034]FIG. 1B illustrates a single tooth from FIG. 1A and defines howtooth movement distances are determined.

[0035]FIG. 1C illustrates the jaw of FIG. 1A together with anincremental position adjustment appliance which has been configuredaccording to the methods of the present invention.

[0036]FIG. 2 is a block diagram illustrating the steps of the presentinvention for producing a system of incremental position adjustmentappliances.

[0037]FIG. 3 is a block diagram setting forth the steps for manipulatingan initial digital data set representing an initial tooth arrangement toproduce a final digital data set corresponding to a desired final tootharrangement.

[0038]FIG. 4 is a flow chart illustrating an eraser tool for the methodsherein.

[0039]FIG. 4A illustrates the volume of space which is being erased bythe program of FIG. 4.

[0040]FIG. 5 is a flow chart illustrating a program for matchinghigh-resolution and low-resolution components in the manipulation ofdata sets of FIG. 3.

[0041]FIG. 6 illustrates the method for generating multiple intermediatedigital data sets which are used for producing the adjustment appliancesof the present invention.

[0042]FIG. 7 illustrates alternative processes for producing a pluralityof appliances according to the methods of the present inventionutilizing digital data sets representing the intermediate and finalappliance designs.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0043] According to the present invention, systems and methods areprovided for incrementally moving teeth using a plurality of discreteappliances, where each appliance successively moves one or more of thepatient's teeth by relatively small amounts. The tooth movements will bethose normally associated with orthodontic treatment, includingtranslation in all three orthogonal directions relative to a verticalcenterline, rotation of the tooth centerline in the two orthodonticdirections (“root angulation” and “torque”), as well as rotation aboutthe centerline.

[0044] Referring now to FIG. 1A, a representative jaw 100 includessixteen teeth 102. The present invention is intended to move at leastsome of these teeth from an initial tooth arrangement to a final tootharrangement. To understand how the teeth may be moved, an arbitrarycenterline (CL) is drawn through one of the teeth 102. With reference tothis centerline (CL), the teeth may be moved in the orthogonaldirections represented by axes 104, 106, and 108 (where 104 is thecenterline). The centerline may be rotated about the axis 108 (rootangulation) and 104 (torque) as indicated by arrows 110 and 112,respectively. Additionally, the tooth may be rotated about thecenterline, as represented by arrow 114. Thus, all possible free-formmotions of the tooth can be performed. Referring now to FIG. 1B, themagnitude of any tooth movement achieved by the methods and devices ofthe present invention will be defined in terms of the maximum lineartranslation of any point P on a tooth 102. Each point Pi will undergo acumulative translation as that tooth is moved in any of the orthogonalor rotational directions defined in FIG. 1A. That is, while the pointwill usually follow a non-linear path, there will be a linear distancebetween any point in the tooth when determined at any two times duringthe treatment. Thus, an arbitrary point P1 may in fact undergo a trueside-to-side translation as indicated by arrow d1, while a secondarbitrary point P2 may travel along an arcuate path, resulting in afinal translation d2. Many aspects of the present invention are definedin terms of the maximum permissible movement of a point Pi induced bythe methods in any particular tooth. Such maximum tooth movement, inturn, is defined as the maximum linear translation of that point Pi onthe tooth which undergoes the maximum movement for that tooth in anytreatment step.

[0045] Referring now to FIG. 1C, systems according to the presentinvention will comprise a plurality of incremental position adjustmentappliances. The appliances are intended to effect incrementalrepositioning of individual teeth in the jaw as described generallyabove. In a broadest sense, the methods of the present invention canemploy any of the known positioners, retainers, or other removableappliances which are known for finishing and maintaining teeth positionsin connection with conventional orthodontic treatment. The systems ofthe present invention, in contrast with prior apparatus and systems,will provide a plurality of such appliances intended to be worn by apatient successively in order to achieve the gradual tooth repositioningas described herein. A preferred appliance 100 will comprise a polymericshell having a cavity shaped to receive and resiliently reposition teethfrom one tooth arrangement to a successive tooth arrangement. Thepolymeric shell will preferably, but not necessarily, fit over all teethpresent in the upper or lower jaw. Often, only certain one(s) of theteeth will be repositioned while others of the teeth will provide a baseor anchor region for holding the repositioning appliance in place as itapplies the resilient repositioning force against the tooth or teeth tobe repositioned. In complex cases, however, many or most of the teethwill be repositioned at some point during the treatment. In such cases,the teeth which are moved can also serve as a base or anchor region forholding the repositioning appliance. Additionally, the gums and/or thepalette can serve as an anchor region, thus allowing all or nearly allof the teeth to be repositioned simultaneously.

[0046] The polymeric appliance 100 of FIG. 1C is preferably formed froma thin sheet of a suitable elastomeric polymeric, such as Tru-Tain 0.03in. thermal forming dental material, Tru-Tain Plastics, Rochester, Minn.55902. Usually, no wires or other means will be provided for holding theappliance in place over the teeth. In some cases, however, it will bedesirable or necessary to provide individual anchors on teeth withcorresponding receptacles or apertures in the appliance 100 so that theappliance can apply an upward force on the tooth which would not bepossible in the absence of such an anchor. Specific methods forproducing the appliances 100 are described hereinafter.

[0047] Referring now to FIG. 2, the overall method of the presentinvention for producing the incremental position adjustment appliancesfor subsequent use by a patient to reposition the patient's teeth willbe described. As a first step, a digital data set representing aninitial tooth arrangement is obtained, referred to hereinafter as theIDDS. The IDDS may be obtained in a variety of ways. For example, thepatient's teeth may be scanned or imaged using well known technology,such as X-rays, three-dimensional X-rays, computer-aided tomographicimages or data sets, magnetic resonance images, etc. Methods fordigitizing such conventional images to produce data sets useful in thepresent invention are well known and described in the patent and medicalliterature. Usually, however, the present invention will rely on firstobtaining a plaster cast of the patient's teeth by well knowntechniques, such as those described in Graber, Orthodontics: Principleand Practice, Second Edition, Saunders, Philadelphia, 1969, pp. 401-415.After the tooth casting is obtained, it can be digitally scanned using aconventional laser scanner or other range acquisition system to producethe IDDS. The data set produced by the range acquisition system may, ofcourse, be converted to other formats to be compatible with the softwarewhich is used for manipulating images within the data set, as describedin more detail below. General techniques for producing plaster casts ofteeth and generating digital models using laser scanning techniques aredescribed, for example, in U.S. Pat. No. 5,605,459, the full disclosureof which is incorporated herein by reference.

[0048] There are a variety of range acquisition systems, generallycategorized by whether the process of acquisition requires contact withthe three dimensional object. A contact-type range acquisition systemutilizes a probe, having multiple degrees of translational and/orrotational freedom. By recording the physical displacement of the probeas it is drawn across the sample surface, a computer-readablerepresentation of the sample object is made. A non-contact-type rangeacquisition device can be either a reflective-type or transmissive-typesystem. There are a variety of reflective systems in use. Some of thesereflective systems utilize non-optical incident energy sources such asmicrowave radar or sonar. Others utilize optical energy. Thosenon-contact-type systems working by reflected optical energy furthercontain special instrumentation configured to permit certain measuringtechniques to be performed (e.g., imaging radar, triangulation andinterferometry).

[0049] A preferred range acquisition system is an optical, reflective,non-contact-type scanner. Non-contact-type scanners are preferredbecause they are inherently nondestructive (i.e., do not damage thesample object), are generally characterized by a higher captureresolution and scan a sample in a relatively short period of time. Onesuch scanner is the Cyberware Model 15 manufactured by Cyberware, Inc.,Monterey, Calif.

[0050] Either non-contact-type or contact-type scanners may also includea color camera, that when synchronized with the scanning capabilities,provides a means for capturing, in digital format, a colorrepresentation of the sample object. The importance of this furtherability to capture not just the shape of the sample object but also itscolor is discussed below.

[0051] The methods of the present invention will rely on manipulatingthe IDDS at a computer or workstation having a suitable graphical userinterface (GUI) and software appropriate for viewing and modifying theimages. Specific aspects of the software will be described in detailhereinafter. While the methods will rely on computer manipulation ofdigital data, the systems of the present invention comprising multipledental appliances having incrementally differing geometries may beproduced by non-computer-aided techniques. For example, plaster castsobtained as described above may be cut using knives, saws, or othercutting tools in order to permit repositioning of individual teethwithin the casting. The disconnected teeth may then be held in place bysoft wax or other malleable material, and a plurality of intermediatetooth arrangements can then be prepared using such a modified plastercasting of the patient's teeth. The different arrangements can be usedto prepare sets of multiple appliances, generally as described below,using pressure and vacuum molding techniques. While such manual creationof the appliance systems of the present invention will generally be muchless preferred, systems so produced will come within the scope of thepresent invention.

[0052] Referring again to FIG. 2, after the IDDS has been obtained, thedigital information will be introduced to the computer or otherworkstation for manipulation. In the preferred approach, individualteeth and other components will be “cut” to permit their individualrepositioning or removal from the digital data. After thus “freeing” thecomponents, the user will often follow a prescription or other writtenspecification provided by the treating professional. Alternatively, theuser may reposition them based on the visual appearance or using rulesand algorithms programmed into the computer. Once the user is satisfiedwith the final arrangement, the final tooth arrangement is incorporatedinto a final digital data set (FDDS).

[0053] Based on both the IDDS and the FDDS, a plurality of intermediatedigital data sets (INTDDS's) are generated to correspond to successiveintermediate tooth arrangements. The system of incremental positionadjustment appliances can then be fabricated based on the INTDDS's, asdescribed in more detail below.

[0054]FIG. 3 illustrates a representative technique for manipulating theIDDS to produce the FDDS on the computer. Usually, the data from thedigital scanner will be in a high resolution form. In order to reducethe computer time necessary to generate images, a parallel set ofdigital data set representing the IDDS at a lower resolution will becreated. The user will manipulate the lower resolution images while thecomputer will update the high resolution data set as necessary. The usercan also view/manipulate the high resolution model if the extra detailprovided in that model is useful. The IDDS will also be converted into aquad edge data structure if not already present in that form. A quadedge data structure is a standard topological data structure defined inPrimitives for the Manipulation of General Subdivisions and theComputation of Voronoi Diagrams, ACM Transactions of Graphics, Vol. 4,No. 2, April 1985, pp. 74-123. Other topological data structures, suchas the winged-edge data structure, could also be used.

[0055] As an initial step, while viewing the three-dimensional image ofthe patient's jaw, including the teeth, gingivae, and other oral tissue,the user will usually delete structure which is unnecessary for imagemanipulation and/or final production of an appliance. These unwantedsections of the model may be removed using an eraser tool to perform asolid modeling subtraction. The tool is represented by a graphic box.The volume to be erased (the dimensions, position, and orientation ofthe box) are set by the user employing the GUI. Typically, unwantedsections would include extraneous gum area and the base of theoriginally scanned cast. Another application for this tool is tostimulate the extraction of teeth and the “shaving down” of toothsurfaces. This is necessary when additional space is needed in the jawfor the final positioning of a tooth to be moved. The treatingprofessional may choose to determine which teeth will be shaved and/orwhich teeth will be extracted. Shaving allows the patient to maintaintheir teeth when only a small amount of space is needed. Typically,extraction and shaving, of course, will be utilized in the treatmentplanning only when the actual patient teeth are to be extracted and/orshaved prior to initiating repositioning according to the methods of thepresent invention.

[0056] Removing unwanted and/or unnecessary sections of the modelincreases data processing speed and enhances the visual display.Unnecessary sections include those not needed for creation of the toothrepositioning appliance. The removal of these unwanted sections reducesthe complexity and size of the digital data set, thus acceleratingmanipulations of the data set and other operations.

[0057] After the user positions and sizes the eraser tool and instructsthe software to erase the unwanted section, all triangles within the boxset by the user will be removed and the border triangles are modified toleave a smooth, linear border. The software deletes all of the triangleswithin the box and clips all triangles which cross the border of thebox. This requires generating new vertices on the border of the box. Theholes created in the model at the faces of the box are re-triangulatedand closed using the newly created vertices.

[0058] The saw tool is used to define the individual teeth (or possiblygroups of teeth) to be moved. The tool separates the scanned image intoindividual graphic components enabling the software to move the tooth orother component images independent of remaining portions of the model.The saw tool defines a path for cutting the graphic image by using twocubic B-spline curves lying in space, possibly constrained to parallelplanes. A set of lines connects the two curves and shows the user thegeneral cutting path. The user may edit the control points on the cubicB-splines, the thickness of the saw cut, and the number of erasers used,as described below.

[0059] Thickness: When a cut is used to separate a tooth, the user willusually want the cut to be as thin as possible. However, the user maywant to make a thicker cut, for example, when shaving down surroundingteeth, as described above. Graphically, the cut appears as the curvebounded by half the thickness of the cut on each side of the curve.

[0060] Number of Erasers: A cut is comprised of multiple eraser boxesarranged next to each other as a piecewise linear approximation of theSaw Tool=s curve path. The user chooses the number of erasers, whichdetermines the sophistication of the curve created—the greater thenumber of segments, the more accurately the cutting will follow thecurve. The number of erasers is shown graphically by the number ofparallel lines connecting the two cubic B-spline curves. Once a saw cuthas been completely specified the user applies the cut to the model. Thecut is performed as a sequence of erasings. A preferred algorithm is setforth in FIG. 4. FIG. 4A shows a single erasing iteration of the cut asdescribed in the algorithm.

[0061] A preview feature may also be provided in the software. Thepreview feature visually displays a saw cut as the two surfaces thatrepresent opposed sides of the cut. This allows the user to consider thefinal cut before applying it to the model data set.

[0062] After the user has completed all desired cutting operations withthe saw tool, multiple graphic solids exist. However, at this point, thesoftware has not determined which triangles of the quad edge datastructure belong to which components. The software chooses a randomstarting point in the data structure and traverses the data structureusing adjacency information to find all of the triangles that areattached to each other, identifying an individual component. Thisprocess is repeated starting with the triangle whose component is notyet determined. Once the entire data structure is traversed, allcomponents have been identified.

[0063] To the user, all changes made to the high resolution model appearto occur simultaneously in the low resolution model, and vice versa.However, there is not a one-to-one correlation between the differentresolution models. Therefore, the computer “matches” the high resolutionand low resolution components as best as it can subject to definedlimits. The algorithm is described in FIG. 5.

[0064] After the teeth and other components have been placed or removedso that the final tooth arrangement has been produced, it is necessaryto generate a treatment plan, as illustrated in FIG. 6. The treatmentplan will ultimately produce the series of INTDDS's and FDDS asdescribed previously. To produce these data sets, it is necessary todefine or map the movement of selected individual teeth from the initialposition to the final position over a series of successive steps. Inaddition, it may be necessary to add other features to the data sets inorder to produce desired features in the treatment appliances. Forexample, it may be desirable to add wax patches to the image in order todefine cavities or recesses for particular purposes. For example, it maybe desirable to maintain a space between the appliance and particularregions of the teeth or jaw in order to reduce soreness of the gums,avoid periodontal problems, allow for a cap, and the like. Additionally,it will often be necessary to provide a receptacle or aperture intendedto accommodate an anchor which is to be placed on a tooth in order topermit the tooth to be manipulated in a manner that requires the anchor,e.g. lifted relative to the jaw.

[0065] Some methods for manufacturing the tooth repositioning appliancesrequire that the separate, repositioned teeth and other components beunified into a single continuous structure in order to permitmanufacturing. In these instances, “wax patches” are used to attachotherwise disconnected components of the INTDDS's. These patches areadded to the data set underneath the teeth and above the gum so thatthey do not effect the geometry of the tooth repositioning appliances.The application software provides for a variety of wax patches to beadded to the model, including boxes and spheres with adjustabledimensions. The wax patches that are added are treated by the softwareas additional pieces of geometry, identical to all other geometries.Thus, the wax patches can be repositioned during the treatment path aswell as the teeth and other components.

[0066] In the manufacturing process, which relies on generation ofpositive models to produce the repositioning appliance, adding a waxpatch to the graphic model will generate a positive mold that has thesame added wax patch geometry. Because the mold is a positive of theteeth and the appliance is a negative of the teeth, when the applianceis formed over the mold, the appliance will also form around the waxpatch that has been added to the mold. When placed in the patient'smouth, the appliance will thus allow for a space between the innercavity surface of the appliance and the patient's teeth or gums.Additionally, the wax patch may be used to form a recess or aperturewithin the appliance which engages an anchor placed on the teeth inorder to move the tooth in directions which could not otherwise beaccomplished.

[0067] In addition to such wax patches, an individual component, usuallya tooth, can be scaled to a smaller or larger size which will result ina manufactured appliance having a tighter or looser fit, respectively.

[0068] Treatment planning is extremely flexible in defining the movementof teeth and other components. The user may change the number oftreatment stages, as well as individually control the path and speed ofcomponents.

[0069] Number of Treatment Stages: The user can change the number ofdesired treatment stages from the initial to the target states of theteeth. Any component that is not moved is assumed to remain stationary,and thus its final position is assumed to be the same as the initialposition (likewise for all intermediate positions, unless one or morekey frames are defined for that component).

[0070] Key frames: The user may also specify “key frames” by selectingan intermediate state and making changes to component position(s).Unless instructed otherwise, the software automatically linearlyinterpolates between all user-specified positions (including the initialposition, all key frame positions, and the target position). Forexample, if only a final position is defined for a particular component,each subsequent stage after the initial stage will simply show thecomponent an equal linear distance and rotation (specified by aquaternion) closer to the final position. If the user specifies two keyframes for that component, it will “move” linearly from the initialposition through different stages to the position defined by the firstkey frame. It will then move, possibly in a different direction,linearly to the position defined by the second key frame. Finally, itwill move, possibly in yet a different direction, linearly to the targetposition.

[0071] The user can also specify non-linear interpolation between thekey frames. A spline curve is used to specify the interpolating functionin a conventional manner.

[0072] These operations may be done independently to each component, sothat a key frame for one component will not affect another component,unless the other component is also moved by the user in that key frame.One component may accelerate along a curve between stages 3 and 8, whileanother moves linearly from stage 1 to 5, and then changes directionsuddenly and slows down along a linear path to stage 10. Thisflexibility allows a great deal of freedom in planning a patient=streatment.

[0073] Lastly, the software may incorporate and the user may at anypoint use a “movie” feature to automatically animate the movement frominitial to target states. This is helpful for visualizing overallcomponent movement throughout the treatment process.

[0074] Above it was described that the preferred user interface forcomponent identification is a three dimensional interactive GUI. Athree-dimensional GUI is also preferred for component manipulation. Suchan interface provides the treating professional or user with instant andvisual interaction with the digital model components. It is preferredover interfaces that permit only simple low-level commands for directingthe computer to manipulate a particular segment. In other words, a GUIadapted for manipulation is preferred over an interface that acceptsdirectives, for example, only of the sort: “translate this component by0.1 mm to the right.” Such low-level commands are useful forfine-tuning, but, if they were the sole interface, the processes ofcomponent manipulation would become a tiresome and time-consuminginteraction.

[0075] Before or during the manipulation process, one or more toothcomponents may be augmented with template models of tooth roots.Manipulation of a tooth model augmented with a root template is useful,for example, in situations where impacting of teeth below the gumline isa concern. These template models could, for example, comprise adigitized representation of the patient's teeth x-rays.

[0076] The software also allows for adding annotations to the datasetswhich can comprise text and/or the sequence number of the apparatus. Theannotation is added as recessed text (i.e. it is 3-D geometry), so thatit will appear on the printed positive model. If the annotation can beplaced on a part of the mouth that will be covered by a repositioningappliance, but is unimportant for the tooth motion, the annotation mayappear on the delivered repositioning appliance(s).

[0077] The above-described component identification and componentmanipulation software is designed to operate at a sophisticationcommensurate with the operator's training level. For example, thecomponent manipulation software can assist a computer operator, lackingorthodontic training, by providing feedback regarding permissible andforbidden manipulations of the teeth. On the other hand, anorthodontist, having greater skill in intraoral physiology andteeth-moving dynamics, can simply use the component identification andmanipulation software as a tool and disable or otherwise ignore theadvice.

[0078] Once the intermediate and final data sets have been created, theappliances may be fabricated as illustrated in FIG. 7. Preferably,fabrication methods will employ a rapid prototyping device 200 such as astereolithography machine. A particularly suitable rapid prototypingmachine is Model SLA-250/50 available from 3D System, Valencia,California. The rapid prototyping machine 200 will selectively harden aliquid or other non-hardened resin into a three-dimensional structurewhich can be separated from the remaining non-hardened resin, washed,and used either directly as the appliance or indirectly as a mold forproducing the appliance. The prototyping machine 200 will receive theindividual digital data sets and produce one structure corresponding toeach of the desired appliances. Generally, because the rapid prototypingmachine 200 may utilize a resin having non-optimum mechanical propertiesand which may not be generally acceptable for patient use, it will bepreferred to use the prototyping machine to produce molds which are, ineffect, positive tooth models of each successive stage of the treatment.After the positive models are prepared, a conventional pressure orvacuum molding machine may be used to produce the appliances from a moresuitable material, such as 0.03 inch thermal forming dental material,available from Tru-Tain Plastics, Rochester, Minn. 55902. Suitablepressure molding equipment is available under the tradename BIOSTAR fromGreat Lakes Orthodontics, Ltd., Tonawanda, N.Y. 14150. The moldingmachine 250 produces each of the appliances directly from the positivetooth model and the desired material. Suitable vacuum molding machinesare available from Raintree Essix, Inc.

[0079] After production, the plurality of appliances which comprise thesystem of the present invention are preferably supplied to the treatingprofessional all at one time. The appliances will be marked in somemanner, typically by sequential numbering directly on the appliances oron tags, pouches, or other items which are affixed to or which encloseeach appliance, to indicate their order of use. Optionally, writteninstructions may accompany the system which set forth that the patientis to wear the individual appliances in the order marked on theappliances or elsewhere in the packaging. Use of the appliances in sucha manner will reposition the patient's teeth progressively toward thefinal tooth arrangement.

[0080] While the above is a complete description of the preferredembodiments of the invention, various alternatives, modifications, andequivalents may be used. Therefore, the above description should not betaken as limiting the scope of the invention which is defined by theappended claims.

What is claimed is:
 1. A method of fabricating a plurality of dentalincremental position adjustment appliances, said method comprising:providing a plurality of positive models of successive tootharrangements, wherein each successive arrangement represents a stageprogressing from an initial tooth arrangement to an intermediate or afinal tooth arrangement; and fabricating the plurality of dentalappliances as negatives of the positive models.
 2. A method as in claim1 , wherein providing said positive models comprises: providing digitaldata representing said plurality of successive tooth arrangements; andcontrolling a fabrication machine to produce said plurality of positivemodels of successive tooth arrangements.
 3. A method as in claim 2 ,wherein providing digital data comprises producing a plurality ofdigital data sets, wherein each set represents one of the successivetooth arrangements.
 4. A method as in claim 2 , wherein controlling thefabrication machine comprises: providing a volume of non-hardenedpolymeric resin; and scanning a laser to selectively harden the resin ina shape corresponding to each of the positive models.
 5. A method as inclaim 3 , wherein controlling the fabrication machine comprises:providing a volume of non-hardened polymeric resin; and scanning a laserto selectively harden the resin in a shape corresponding to each of thepositive models.
 6. A method as in claim 1 , wherein producing thedental appliances comprises molding a thin polymeric sheet over each ofthe positive models to produce a plurality of thin polymeric shells. 7.A method of fabricating one or more dental incremental positionadjustment appliances, comprising: providing a computer generatedpositive model of at least one tooth arrangement selected from aninitial tooth arrangement, an intermediate tooth arrangement, and finaltooth arrangement; and fabricating at least one dental appliance as anegative of the computer generated positive model.
 8. A method as inclaim 7 , wherein providing said at least one positive model comprises:providing digital data representing at least one tooth arrangement; andcontrolling a fabrication machine to produce said at least one positivemodel of a tooth arrangement.
 9. A method as in claim 8 , whereinproviding digital data comprises producing a plurality of digital datasets, wherein each set represents one of a plurality of successive tootharrangements.
 10. A method as in claim 8 , wherein controlling thefabrication machine comprises: providing a volume of non-hardenedpolymeric resin; and scanning a laser to selectively harden the resin ina shape corresponding to each of the positive models.
 11. A method as inclaim 9 , wherein controlling the fabrication machine comprises:providing a volume of non-hardened polymeric resin; and scanning a laserto selectively harden the resin in a shape corresponding to each of thepositive models.
 12. A method as in claim 7 , wherein fabricating the atleast one dental appliance comprises molding a thin polymeric sheet oversaid at least one positive model to produce at least one thin polymericshells.